1. Field of the Invention:
The present invention relates to improved diorganopolysiloxane compositions which are stable in storage in the absence of moisture and curable into self-adhesive elastomeric state in the presence of moisture, and, more especially, to such improved compositions comprising an .alpha.,.omega.-dihydroxydiorganopolysiloxane polymer, a ketiminoxysilane crosslinking agent therefor, and a tackifying agent, or tackifier, which comprises a (.DELTA..sup.2 -imidazolinyl)alkylsilane or a diorganopolysiloxane copolymer containing (.DELTA..sup.2 -imidazolinyl)alkylsiloxane recurring units.
2. Description of the Prior Art:
Single-component organopolysiloxane compositions comprising a ketiminoxysilane crosslinking agent, typically also containing an inorganic filler and a curing catalyst, have long been known to this art. They are described, for example, in French Pat. Nos. 1,314,649 and 1,371,250, U.S. Pat. Nos. 3,678,003 and 3,986,999, British Pat. No. 1,468,467, Belgian Pat. No. 901,479 and European Pat. No. EP-A-157,580.
Such compositions are widely used for coating and jointing applications, and in particular as a sealant in the construction industry for producing glazed structures.
In this particular application, the cured elastomer should have a relatively low elastic modulus and should, above all, adhere strongly to glass and to the material forming the structure into which the glass is sealed, such as timber, aluminum, concrete, PVC (polyvinyl chloride), natural and synthetic rubbers, stone, earthenware and brick.
However, the elastomers produced from compositions containing a ketiminoxysilane crosslinking agent generally display inadequate adhesion to materials used in the building construction industry. Indeed, various additives to be incorporated into such compositions in order to overcome this deficiency have already been proposed to this art.
Thus, Belgian Pat. No. 901,479 proposes the use of titanium complexes, certain of which are, furthermore, claimed as crosslinking catalysts in French Pat. No. 2,531,095.
French Pat. No. 2,074,144 describes using a silane as a tackifier, each molecule of which contains at least one amino group linked to silicon by at least one carbon atom, and at least one monovalent hydrocarbon radical optionally bearing an amino or alkoxy group as a substituent and linked to the silicon via an oxygen atom. Furthermore, tackifiers are also known which are polyalkoxysilanes (see, in particular, European Pat. No. EP-A-021,859). These tackifiers are described as having no effect on the storage stability of the curable starting materials capable of yielding elastomers, without, however, being less effective.
Typical examples of this class of tackifiers are the following: (C.sub.2 H.sub.5 O).sub.3 Si(CH.sub.2).sub.3 NH.sub.2 or .gamma.-aminopropyltriethoxysilane; CH.sub.3 (C.sub.2 H.sub.5 O).sub.2 Si(CH.sub.2).sub.3 NH.sub.2 or .gamma.-aminopropylmethyldiethoxysilane; (CH.sub.3)(CH.sub.3 O).sub.2 Si(CH.sub.2).sub.3 NH(CH.sub.2).sub.2 NH.sub.2 or .beta.-aminoethyl-.gamma.-aminopropylmethyldimethoxysilane.
Given that this class of tackifiers possesses the characteristics referred to above for the two types of compositions containing a polyalkoxysilane and ketiminoxysilane crosslinking agent, one skilled in this art would conclude that all the tackifiers described earlier for use with one type would also be adapted for use with the other type, as, for example, the silane of the formula: ##STR1## or .gamma.-morpholinopropyltriethoxysilane, described as a tackifier for compositions containing a polyalkoxysilane crosslinking agent in French Pat. No. 2,572,415.
However, as is shown in the comparative examples below, it appears that the tackifiers of the prior art have at least one of the following disadvantages, in compositions containing a ketiminoxysilane crosslinking agent:
1. the storage stability of the compositions is adversely affected by the presence of the tackifier;
2. the crosslinking of the compositions into an elastomer is too slow, particularly at ambient temperature;
3. the tackifier does not render the elastomer sufficiently adhesive; and
4. the physical properties of the elastomer are mediocre or clearly inadequate, in particular for jointing applications.